Process for production of fatty acid esters

ABSTRACT

A process for producing C1-C4 alkyl esters of fatty acids comprising the steps of: (a) reacting glycerine with a glyceride mixture containing levels of free fatty acids which inhibit trans-esterification with alkaline catalysts until the level of free fatty acids is reduced sufficiently to enable the use of an alkaline trans-esterification catalyst; (b) reacting the mixture resulting from step (a) with one or more alkaline trans-esterification catalysts and one or more C1-C4 alcohols until a mixture of one or more C1-C4 alkyl esters of fatty acids and crude glycerine forms; (c) recovering the one or more C1-C4 alkyl esters of fatty acids; and (d) recovering the crude glycerine, wherein at least a portion of the crude glycerine recovered in step (d) is used in step (a) of a subsequent process.

FIELD OF THE INVENTION

The invention relates to a process for production of esters of fattyacids. More particularly, it relates to a cost-effective process forproduction of esters of fatty acids from glycerides which contain highlevels of free fatty acids.

BACKGROUND OF THE INVENTION

In this specification, where a document, act or item of knowledge isreferred to or discussed, this reference or discussion is not anadmission that the document, act or item of knowledge or any combinationthereof was at the priority date:

(a) part of common general knowledge; or

(b) known to be relevant to an attempt to solve any problem with whichthis specification is concerned.

Esters of fatty acids are useful chemicals in many areas of industry andhave generated much interest as alternative fuels in recent times. Suchesters are often produced by the trans-esterification of triglyceridesfrom animal or vegetable sources with C1-C4 alcohols to produce C1-C4alkyl esters of fatty acids, along with crude glycerine released as aby-product. A variety of catalysts, including acidic catalysts, enzymes,metal salts or alkaline catalysts, are available fortrans-esterification. The alkaline catalysts such as sodium or potassiumhydroxides or alkoxides are preferred because they are efficient, easilyseparated from the product and compatible with conventional reactorsystems.

It is known that triglyceride mixtures from animal or vegetable sourcescontain free fatty acids (FFA) as well as mono- and di-glycerides. Oilswhich are crude or old, such as gut tallow or used frying oils, oftenhave higher levels of FFA. The term “glyceride mixture” is used in thisdescription to refer to fatty materials containing mono-, di- andtri-glycerides as well as FFA.

If there are high levels of FFA in the glyceride mixture, that is levelsgreater than 4%, difficulties can result in the trans-esterificationprocess since the FFA will react with alkaline catalysts to form soaps.These soaps not only cause deactivation of the catalyst but also causeadditional problems during further processing and purifying of the C1-C4alkyl esters of fatty acids, because they tend to limit the release ofcrude glycerine and generate emulsion phases during washing cycles. Thelevel of FFA in the glyceride mixture should be below about 4% andpreferably below about 2% by weight to enable alkalinetrans-esterification to take place efficiently.

It is possible to lower the FFA content of a glyceride mixture by alkalirefining prior to trans-esterification , whereby the FFAs areselectively removed from the glyceride mixture as water soluble soaps.However, whilst alkali refining is suitable for removal of small amountsof FFA, oils with higher levels of FFA are not suited to this processbecause of high yield losses and poor phase separations associated withsoapy emulsions.

Another attempt to lower the FFA content is disclosed in UK patent no612,667. The process disclosed involves the conversion of substantiallyall of the fatty acid components into lower alkyl esters using an acidiccatalyst. The process described is typical of acid catalysedtrans-esterification processes in that it (1) requires a very largeexcess of alcohol which is not economical, (2) is not compatible withsteel based reactor systems and (3) results in ester products whichcontain high levels of undesired FFA which can be removed by alkalirefining but this process is inefficient by commercial standards.

Other attempts to reduce FFA content have involved the use of enzymes,in particular lipase, however these attempts have not provided resultswhich are commercially acceptable.

There is thus a need for an efficient process for reducing high levelsof free fatty acids in glyceride mixtures to enable the glyceridemixtures to be reacted with C1 to C4 alcohols in the presence ofalkaline catalysts to produce C1-C4 alkyl esters of fatty acids.

SUMMARY OF THE INVENTION

It has been found that if a glyceride mixture containing levels of FFAwhich inhibit trans-esterification with alkaline catalysts is reactedwith glycerine (which is available as a by-product from this process)prior to adding the C1-C4 alcohol and catalyst, the FFAs can be reducedto a level which enables the efficient use of alkalinetrans-esterification catalysts.

According to the invention there is provided a process for producingC1-C4 alkyl esters of fatty acids comprising the steps of:

(a) reacting glycerine with a glyceride mixture containing levels offree fatty acids which inhibit trans-esterification by alkalinetrans-esterification catalysts until the level of free fatty acids isreduced sufficiently to enable the use of an alkalinetrans-esterification catalyst;

(b) reacting the mixture resulting from step (a) with one or morealkaline trans-esterification catalysts and one or more C1-C4 alcoholsuntil a mixture of one or more C1-C4 alkyl esters of fatty acids andcrude glycerine forms;

(c) recovering the one or more C1-C4 alkyl esters of fatty acids; and

(d) recovering the crude glycerine

wherein at least a portion of the crude glycerine recovered in step (d)is used in step (a) of a subsequent process.

The glyceride mixture may be any such mixture known to those skilled inthe art, including glycerides of animal, vegetable or synthetic origin.The glyceride mixture may be selected from virgin fatty products such ascrude or refined tallow or vegetable oils or from used materials such asyellow grease (used frying oil) or acid oils (by-product of soap, oilprocessing industries or from this process). The levels of free fattyacids which inhibit trans-esterification with alkaline catalysts areknown to those skilled in the art. Typically, the glyceride mixture usedin the process according to the invention contains levels of FFA greaterthan 4% by weight of the glyceride mixture. Preferably the levels of FFAare in the range of from 4 to 75% by weight. More preferably, the levelsof FFA are in the range of from 4 to 30% by weight.

The word “glycerine” when used in the context of step (a) refers to anyglycerine containing mixture including crude glycerine recovered fromstep (d) which consists of more than 50% by weight glycerine. Theglycerine may also contain some soap, alcohol and other fatty material.Mineral salts and acids are undesirable in the glycerine as they mayinhibit the reaction or adversely affect the processing equipment.

The amount of crude glycerine recovered in step (d) is likely to besignificantly larger than the amount required in step (a) and thus onlythe amount required will be used. Any excess crude glycerine recoveredfrom step (d) may be stored for later use, used in another process orelse sold. In some instances, the amount of contaminants in the crudeglycerine recovered from step (d) may make it unsuitable as the solesource of glycerine in step (a) and it will be necessary to use someglycerine from another source. For example, if the glyceride mixture hada very high level of FFA then it would not be appropriate to use solelycrude glycerine recovered from step (d) which had high levels ofcontaminants.

The amount of glycerine used in step (a) will depend on the level of FFAin the glyceride mixture. Typically for each 1% by weight of FFA in theglyceride mixture, 0.1 to 0.5% by weight of available glycerine would berequired to reduce the FFA to below 2% by weight. Preferably, the amountof available glycerine is about 0.2% by weight for each 1% by weight ofFFA in the glyceride mixture. Once the glyceride mixture contains lessthan 2% by weight FFA then an alkaline trans-esterification catalyst maybe used. If the glyceride mixture contains alkyl esters of fatty acidsthen such alkyl esters should be considered as FFA when calculating therequired amount of glycerine. This is because the alkyl ester may reactwith the glycerine to form glyceride releasing the alcohol which may bedistilled from the reaction mixture with the water vapour.

A person skilled in the art will know that the reaction in step (a) maybe conducted under a variety of temperature and pressure conditions. Forexample a temperature above about 180° C. at reduced pressure iscommonly used to aid the removal of water produced during the reaction.Another example of suitable conditions for the reaction in step (a) is atemperature of about 220° C. at ambient pressure. The use of anunreactive atmosphere (eg nitrogen) or agitation of the reaction mixturemay be useful to assist in the removal of water from the reaction.Optionally, a solvent may be added to the mixture to form a constantboiling azeotrope to assist removal of water.

A person skilled in the art will know that the reaction in step (b) maybe conducted under a variety of temperature and pressure conditions. Forexample a temperature in the range from 75 to 85° C. at ambient pressureis commonly applied for one hour with agitation. Increased pressure mayenable the reaction to proceed more quickly or completely. The reactionmay then be left to rest to allow the crude glycerine to separate out bygravity or alternatively the crude glycerine may be separated bycentrifugal separation or by plate separation.

A person skilled in the art will know of procedures for recovering theC1-C4 alkyl esters of fatty acids and crude glycerine in steps (c) and(d). For example, the mixture from step (b) may be left for two hourswithout agitation during which time the mixture will separate into twolayers. The denser layer will be the crude glycerine (which is suitablefor use as glycerine in (a)) and the lighter layer the C1-C4 alkylesters of fatty acids. Typically the amount of crude glycerine generatedfrom this process is more than is required for re-use in step (a) of asubsequent process and the amount of C1-C4 alkyl esters of fatty acidsrecovered is similar to the quantity of the original glyceride mixture.

Once separated, these products may then be used directly in this oranother process or else purified according to standard procedures forsale or another use. For example, the crude glycerine may be acidified,defatted and (partially or completely) dried. Steam distillation and/orvacuum distillation and/or carbon decolourisation may be used to improvethe glycerine. The fatty ester may be further reacted, water washed,dried, deodorised, distilled or decolourised.

Suitable alkaline trans-esterification catalysts are known to thoseskilled in the art and include sodium or potassium alkoxides orhydroxides. Alkoxides are preferred due to speed and efficiency ofreaction. Typically, the amount of alkaline catalyst required to effecttrans-esterification is in the range from 0.2 to 2% by weight of theglyceride mixture.

C1-C4 alcohols which are suitable for use in the process of theinvention will be known to those skilled in the art. For example,methanol or ethanol may be used. A minimum of three moles of C1-C4alcohol to each mole of triglyceride (assuming that the glyceridemixture with now low FFA is predominantly triglyceride) is required toeffect the trans-esterification. Typically excess alcohol is used inthis process to ensure completeness of reaction. Excess alcohol may berecovered from the mixture for reuse. Alternatively, the alcohol andalkaline catalyst can be reacted with the glyceride mixture more thanonce with removal of crude glycerine between applications.

In a preferred embodiment, any fatty glycerides or FFA recovered frompurification of the C1-C4 alkyl esters of fatty acids (eg extracted fromwater washings) or from the crude glycerine can be appropriately treated(acidified and washed) and used as part of the glyceride mixture of asubsequent process according to the invention.

DESCRIPTION OF THE DRAWING

The invention will now be further described with reference to FIG. 1which is a flowchart showing one embodiment of a process according tothe invention.

DETAILED DESCRIPTION OF THE DRAWING

In this embodiment, the process starts with a glyceride mixturecontaining levels of FFA which inhibit trans-esterification withalkaline catalysts, for example, about 20% by weight FFA. Examples ofsuch glyceride mixtures are gut tallow or used frying oil.

The glyceride mixture was reacted with crude glycerine at a temperatureabove 180° C. and under reduced pressure until the level of FFA wasbelow 2% by weight.

The mixture was then cooled to 75 to 85° C. and one or more anhydrousC1-C4 alcohols were added, for example ethanol, with an alkalinetrans-esterification catalyst such as sodium methoxide. This mixture wasthen reacted at a temperature in the range of 75 to 85° C. for one hourwith agitation. The reaction was then left to rest for two hours withoutagitation to allow the crude glycerine to separate as the denser phasewhich was then removed. This crude glycerine is a useful by-product,some of which was then used to react with further glyceride mixturecontaining high levels of FFA in a subsequent process. The rest may bestored, sold or used in another process.

The C1-C4 alkyl esters of fatty acids were then purified by removal ofexcess alcohol and catalyst, water washed and then dried.

While the process described here is indicative of a batch process, theseparation and return of a portion of crude glycerine to react with thefeedstock would be equally valid for a continuous or semi-continuousprocess.

EXAMPLES

The invention will now be further explained and illustrated by referenceto the following non-limiting examples.

Example 1

Components Properties Glyceride Mixture Crude tallow mixture with 20%FFA and 5% unsaponifiables Glycerine Crude Glycerine derived fromtrans-esterification of ethyl canolate comprising 85% glycerine AlcoholMethylated Spirits 100SG:F3 ex CSR Distilleries Ethanol with 2% addedmethanol with maximum water content of 0.5%. Catalyst 30% SodiumMethylate in Methanol ex BASFReduction of FFA

Glyceride mixture (180 kg) was reacted with the crude glycerine (100 kg)at 200-220° C. for 12 hours at ambient pressure with gentle nitrogensparge in which time the level of FFA decreased from 20 to 4.3%.Additional crude glycerine (20 kg) was added and the reaction continuedin the same temperature range for a further 8 hours to give a level ofFFA of 2.7%. Again crude glycerine (20 kg) was added and a further 8hours reaction resulted in a level of FFA of 1.8%.

Trans-Esterification with Alcohol

The resultant glyceride mixture with a level of FFA of 1.8% (approx 1920kg) was reacted with methylated spirits (300 kg) and sodium methylatesolution (58 kg) at 75-80° C. for 1 hour. The reaction mixture wasallowed to stand for 2 hours and then crude glycerine (320 kg) wasseparated off by gravity.

The resultant mixture of ethyl and methyl esters of fatty acids wasreacted with additional methylated spirits (80 kg) and sodium methylatesolution (16 kg) at 75-80° C. for 1 hour in order to convert anyremaining unreacted glycerides to fatty ester. The reaction mixture wasthen subjected to a series of water washes to remove soap, FFA, catalystand other impurities then dried at 130° C. and ambient pressure to givea mixture of mixture of ethyl and methyl esters of fatty acids suitablefor use as biodiesel. (Note that the washing process was not optimised.The efficiency of this process was compromised by the high level ofunsaponifiables in the glyceride mixture.)

Results DIN* 51606 Septem- ber 1997 Test Unit Method spec. Results FlashPoint ° C. ASTM D93 min 110 186 Density g/mL ASTM D4052 0.875- 0.87450.90 Water Content Ppm ASTM E1064 max 300 493 Ash % wt ASTM D482 0.030.0250 BS & W % vol ASTM D1796 <0.01 Viscosity cSt ASTM D445 3.5-5.05.41 @40° C. CFPP ° C. IP 309 summer 0 +9 winter −20 Sulphur % wt ASTM D4294 0.01 <0.01 Carbon Residue % wt ASTM D524 0.047 Particulate mg/LASTM D5452* 20 mg/kg 16.5 Contamination Copper degree of ASTM D130 1 1aCorrosion corrosion Neutralisation mgKOH/g ASTM D974 max 0.5 0.45 NumberIodine Number — AOCS Cd 1d-92 max 115 43 Phosphorus mg/kg ASTM D3231 max10 <0.2 Alkali Content mg/kg (1) Max 5 <2 (Na + K)*Note that standards vary from country to country and are regularlybeing revised. The DIN standard relates typically to methyl esters ofrapeseed oil and may not be applicable to alkyl esters derived fromother feedstock.

Example 2

Components Properties Glyceride Mixture Crude tallow mixture with 22%FFA and 0.85% unsaponifiables Glycerine Crude Glycerine derived fromtransesterification of ethyl canolate comprising 80.5% glycerine and 52mg/g alkali calculated as KOH Alcohol Methylated Spirits 100SG:F3 ex CSRDistilleries Ethanol with 2% added methanol with maximum water contentof 0.5%. Catalyst 30% Sodium Methylate in Methanol ex BASFReaction ProcessReduction of FFA

Glyceride mixture (1000 g) was reacted with the crude glycerine (45 g)at 220-240° C. for 3 hours at ambient pressure with gentle nitrogensparge in which time the level of FFA decreased from 22 to 4.0%.Reaction proceeded with vacuum applied for further 3 hours resulting in1016 g of glyceride mixture with a level of FFA of 1.0%.

Trans-Esterification with Alcohol

The resultant glyceride mixture (1016 g with a level of FFA of 1.0%) wasreacted with methylated spirits (167 g) and sodium methylate solution(28 g) at 75-80° C. for 1 hour. The reaction mixture was allowed tostand for 2 hours and then crude glycerine (235 g) was separated off bygravity.

The resultant mixture of ethyl and methyl esters of fatty acids wasreacted with additional methylated spirits (40 g) and sodium methylatesolution (9 g) at 75-80° C. for 1 hour in order to convert any remainingunreacted glycerides to fatty ester. The reaction mixture was thensubjected to a series of water washes to remove soap, FFA, catalyst andother impurities then dried at 130° C. and ambient pressure to give amixture of ethyl and methyl esters of fatty acids (774 g) suitable foruse as biodiesel.

Results Test Unit Result Acid Value mgKOH/g 0.2 Moisture % w/w 0.02%Clarity@20 C. N/A Clear and Bright SG@20 C. g/ml 0.867 Colour (Gardner)N/A 5 FTIR N/A matches ethyl tallowate

The word ‘comprising’ and forms of the word ‘comprising’ as used in thisdescription does not limit the invention claimed to exclude any variantsor additions.

Modifications and improvements to the invention will be readily apparentto those skilled in the art. Such modifications and improvements areintended to be within the scope of this invention.

1. A process for producing C1-C4 alkyl esters of fatty acids comprisingthe steps of: (a) reacting glycerine with a glyceride mixture containinglevels of free fatty acids which inhibit trans-esterification byalkaline trans-esterification catalysts until the level of free fattyacids is reduced sufficiently to enable the use of an alkalinetrans-esterification catalyst; (b) reacting the mixture resulting fromstep (a) with one or more alkaline trans-esterification catalysts andone or more C1-C4 alcohols until a mixture of one or more C1-C4 alkylesters of fatty acids and crude glycerine forms; (c) recovering the oneor more C1-C4 alkyl esters of fatty acids; and (d) recovering the crudeglycerine wherein at least a portion of the crude glycerine recovered instep (d) is used in step (a) of a subsequent process.
 2. A processaccording to claim 1 wherein the glyceride mixture is selected from thegroup consisting of virgin fatty products such as crude or refinedtallow or vegetable oils, from used materials such as yellow grease oracid oils, and mixtures thereof.
 3. A process according to claim 1wherein the glyceride mixture contains levels of free fatty acids equalto or greater than 4% by weight.
 4. A process according to claim 3wherein the glyceride mixture contains levels of free fatty acids in therange from 4 to 75% by weight.
 5. A process according to claim 4 whereinthe glyceride mixture contains levels of free fatty acids in the rangefrom 4 to 30% by weight.
 6. A process according to claim 1 wherein thelevel of free fatty acid in step (a) is reduced to less than 2% byweight.
 7. A process according to claim 1 wherein the ratio of freefatty acid in the glyceride mixture to glycerine is in the range of from1:0.1 to 1:0.5 by weight.
 8. A process according to claim 7 wherein theratio of free fatty acid in the glyceride mixture to glycerine is 1:0.2by weight.
 9. A process according to claim 1 wherein step (a) occurs ata temperature above about 180° C. and at a reduced pressure.
 10. Aprocess according to claim 1 wherein step (a) occurs at a temperature atabout 220° C. and at ambient pressure.
 11. A process according to claim1 wherein agitation is used in step (a) to assist in removal of waterfrom the reaction mixture.
 12. A process according to claim 1 wherein anunreactive atmosphere is used in step (a).
 13. A process according toclaim 1 wherein step (b) occurs at a temperature in the range from 75 to85° C., at ambient pressure for one hour with agitation.
 14. A processaccording to claim 1 wherein steps (c) and (d) occur using gravity toseparate the crude glycerine and C1-C4 alkyl esters of fatty acids intotwo layers which are then recovered.
 15. A process according to claim 1wherein steps (c) and (d) occur using centrifugal separation to separatethe crude glycerine and C1-C4 alkyl esters of fatty acids which are thenrecovered.
 16. A process according to claim 1 wherein steps (c) and (d)occur using plate separation to separate the crude glycerine and C1-C4alkyl esters of fatty acids which are then recovered.
 17. A processaccording to claim 1 wherein the C1-C4 alcohol is selected from thegroup consisting of methanol, ethanol and mixtures thereof.
 18. Aprocess according to claim 1 wherein the amount of C1-C4 alcohols is inexcess of three moles of C1-C4 alcohol to each mole of glyceride.
 19. Aprocess according to claim 1 wherein the alkaline trans-esterificationcatalyst is an alkoxide or hydroxide.
 20. A process according to claim19 wherein the alkaline trans-esterification catalyst is an alkoxide.21. A process according to any one of the preceding claims claim 1wherein the amount of alkaline trans-esterification catalyst is in therange of 0.2 to 2% by weight of the glyceride mixture.
 22. A processaccording to any one of the preceding claims claim 1 wherein the excesscrude glycerine recovered in step (d) is further purified for sale oranother use.